Additive manufacturing (AM) processes have revolutionized the digital design and manufacturing landscape. Extremely complex structures with customized material gradation, the likes of which heretofore were deemed non-manufacturable using traditional manufacturing techniques, are now possible. AM also permits the manufacturing of more complex and efficient infill structures than would otherwise be impossible. Nevertheless, subtractive manufacturing (SM) remains relevant for producing high-precision mechanical parts. Although AM affords wide freedom in customizing the internal structures of parts, SM can achieve finer precision and surface quality specifications than possible with AM, such as needed for functional interfaces requiring high-tolerance fit and assembly.
Historically, the manufacturing of parts from raw stock or material has involved these two distinct, albeit combinable, manufacturing processes. Fabricating a part through SM involves progressively removing or machining material from raw stock until the part has been reduced to the desired form within a specified tolerance. Raw material is often removed by turning, drilling, or milling. Fabricating a part through AM involves progressively adding or depositing material onto a part being fabricated, often by adding successive layers, until the part approximates an intended shape and size, such as used with three-dimensional printing through fused deposition modeling (FDM). For instance, metal AM is sometimes used in lieu of traditional metalworking, such as casting, but with substantially more freedom in generating complex forms, to produce a near-net shape that is close enough to the final part, although functional interfaces may still need to be finished using SM to satisfy tolerancing and surface quality specifications. In many cases, in layer-by-layer AM processes such as FDM, to allow the upper layers to extend beyond the lower layers' width without sagging due to gravity, additional support materials are printed into the lower layers of the near-net shape, which may require SM post-processing to remove, for instance, in metal AM. One approach to removing support structures from a near-net shape is described in U.S. Ser. No. 15/858,520, filed on Dec. 29, 2017 the disclosure of which is incorporated by reference.
Process plans that contain unimodal manufacturing sequences of either purely AM or purely SM processes have state transitions that constitute a partial ordering in terms of set inclusion. At each intermediate state of manufacturing, the physical space occupied by the part being fabricated either increases (for AM-only sequences) or decreases (for SM only-sequences) in size, and every later state respectively either includes or is included within the preceding states in the unimodal sequence. The final outcome of the operations that model the monotonic material deposition (AM) or removal (SM) of such sequences is therefore insensitive to permutations, that is, same steps applied in different orders, even though the intermediate states may vary. If the manufacturing primitives are defined as the geometric model of the material deposited (AM) or removed (SM) at a unit manufacturing action with a given manufacturing instrument with certain degrees of freedom (DOF), the total material deposition (AM) or removal (SM) can be evaluated, irrespective of the order of execution of each AM or SM process within the unimodal sequence. Therefore, the manufacturability of the part can be evaluated before proceeding to computationally expensive process planning to find a specific ordered unimodal sequence of AM or SM actions.
Conventionally, unimodal manufacturing sequences have been the default (and only) modality for AM-only or SM-only machine process plans. Recently, hybrid machines equipped with both AM and SM capabilities have emerged, including the Integrex i-400AM, manufactured by Yamazaki Mazak Corporation, Oguchi, Aichi Prefecture, Japan. Such hybrid machines are not restricted to unimodal sequencing of actions and offer the potential to blend arbitrary combinations of AM and SM modalities, where, for instance, an SM operation may be followed by an AM operation followed by an SM operation, and so on. In turn, these arbitrary multimodal sequences can result in increased manufacturing efficiency and further expands the realm of manufacturing possibilities.
Generating process plans for arbitrary multimodal sequences in hybrid manufacturing, though, remains a challenge. The changes in the physical size of a partially-manufactured part while progressing through an arbitrarily-ordered multimodal sequence of AM and SM actions lacks the monotonicity found in unimodal sequences, and the individual AM and SM operations that model the material deposition and subtraction are sensitive to permutations when mixed with each other. As a result, the order of execution of the AM and SM actions matters, and full process planning for any ordered multimodal sequence appears necessary because the constituent AM and SM actions cannot be evaluated out of sequence. This result comes at potentially significant computational expense due to the enormity of the state transition problem space that needs to be explored. Moreover, the manufacturability of the part could not be guaranteed without first completing the process planning.
Therefore, a need exists for an efficient approach to planning nontrivial hybrid multimodal process plans.